A. Field of the Invention
The present invention is related to a boss of a front cover of a torque converter and a method for producing the boss.
B. Description of Related Art
A torque converter is a device having three types of fluid engaging elements, an impeller, a turbine, and a stator all of which are disposed within a housing. Torque is transmitted by the torque converter from the impeller to the turbine by movement of hydraulic fluid within the housing. The impeller is fixed to a front cover, the impeller and the front cover defining the torque convertor housing. The front cover is connected to a rotary body such as a flex-plate on a engine side and torque is transmitted to a transmission side by means of the hydraulic fluid moving from the impeller to the turbine.
Conventionally, the front cover is joined by via a welding process to a centering boss, the boss being formed by press processing and then welded to a central portion of the front cover. Prior to being joined with the boss, a central portion of the front cover is cut out and is discarded as scrap. The boss is required for positioning and aligning the front cover and torque convertor with the flex plate on the engine side.
Alternatively, a front cover is contemplated wherein an integrated boss is formed by a press processing at the center of the front cover such that the front cover and the boss are unitarily formed from a single material. Thus, the welding process is avoided. The unitary configuration where the boss and the front cover are integrally formed from a single material reduces the number of parts. The unitary configuration also reduces material waste; improves material yield by making it unnecessary to cut a central portion of the front cover out; eliminates scraps cut from the inner peripheral portion of the front cover; eliminates the need for the welding process; and provide stable airtight characteristics because there are no welded portions.
In order to form the above-mentioned unitary configuration of the front cover and boss, several steps must be carried out. For example, to form a boss 90a of a front cover 90, as shown in FIG. 5, a number of steps must be carried out. First, a first preliminary pressing or deforming process is carried out on a disc-shaped material 91, shown in dotted lines in FIG. 6. A center portion 91a of the disc-shaped material 91 is deformed to form a first indentation 91b, as is indicated by the solid lines in FIG. 6. It should be understood that the disc-shaped material 91 subsequently forms the front cover 90 depicted in FIG. 5. Next, the first indentation 91b is further deformed in another pressing step to form a second indentation 91c (shown in FIG. 7) having a more rounded shape that is closer to the shape of the final boss 90a. Next, a finishing pressing process is carried out forming a third indentation 91d (shown in FIG. 8) that is still closer to the shape of the final boss 90a. Lastly, the boss is subjected to machining, such as milling, cutting and/or grinding such that the portions A, B shown in FIG. 9 are formed to define the finished boss 90a. The portions A and B are required for positioning and alignment between the front cover and parts on the engine side.
However, if the boss 90a is formed on the front cover by means of a pressing process where deformation of a material forms the boss, as described above, the radius of the boss 90a is large. Therefore, after machining the thickness of the boss 90a at some positions of the portions A and B is undesirably thin. In particular, proximate the central axis the boss is thin and at a step portion of the portion B the boss also thin. Therefore, the strength of the boss 90a and the front cover 90 is weakened due to the thin portions of the boss 90a.